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Physical Cosmology Dr Ian Parry Tel: 01223 337092 Room: H57 E-mail: [email protected] Lectures: Mon 10am, Thurs 10am HANDOUTS • www.ast.cam.ac.uk/~irp/teaching • Username: intro • Password: dotzenblobs Physical Cosmology Course Schedule What is cosmology about? Cosmology from Greek s world s word, reasoning, theory Physical Cosmology studies the Universe as a whole, draws on many branches of Physics. It tries to explain the following properties of the Universe: • • • • geometry, dynamics content (baryons, photons, neutrinos, dark matter, dark energy) spatial distribution time evolution (thermal history, growth of structure, galaxy formation) Text books http://www.nap.edu/readingroom/books/cosmology http://www.nap.edu/readingroom/books/cosmology Sequence of events • At z=1100 the Universe has cooled down to 3000K . Hydrogen becomes neutral (“Recombination”). • At z <~ 20 the “first” star (clusters)/small galaxies form. • At z ~ 6-10 these gradually photo-ionize the hydrogen in the IGM (“Reionization”). • At z<6 galaxies form most of their stars and grow by merging. • At z<1 massive galaxy clusters are assembled. The whole sky as seen by WMAP WMAP = Wilkinson Microwave Anisotropy Probe The Standard Model Cosmology – early history “The Greeks” Aristotle (384-322 BC) Ptolemy (100-170) “The Renaissance” Copernicus (1473-1543) Brahe (1546-1601) Kepler (1571-1630) Galileo (1546-1642) Newton (1643-1727) geocentric cosmology heavenly bodies move on spheres epicycles Earth not at the centre of the Universe (Copernican principle) detects supernova, measures planetary motion elliptic planetary motion, Kepler’s laws observes planets with telescope detects moons of Jupiter calculus, Newton’s laws, mechanics, deterministic cosmology Cosmology – history continued 1683 Newton’s Principia 1750 Structure of Milky Way (Wright, Kant, Herschel) 1915 1927 George Lemaitre proposed the “primeval atom”: expansion implies a singularity in the past 1948 Nucleosynthesis of light elements in early universe and prediction of the CMB (Gamow, Alpha, Herman) 1948 Steady-state theory proposed (Hoyle, Bondi, Gold) 1949 Hoyle coins phrase “big bang” Einstein’s General relativity 1916/7 Relativistic Cosmologies (Einstein, Friedman, Lemaitre, de Sitter) 1920 Curtis/Shapley debate on galaxies 1957 Nucleosynthesis of heavy elements (Burbidge, Burbidge, Hoyle, Fowler) 1924 Hubble establishes Andromeda nebula to be extragalactic 1965 Cosmic microwave background (CMB) discovered (Penzias, Wilson) Late 1920’s Expansion of Universe established, Hubble’s law Cosmology – recent history 1980’s Hot/Cold Dark Matter; Large Scale Structure in galaxy distribution measured 1992 Detection of CMB fluctuations by COBE satellite late 1990s increasing observational evidence for cosmological constant/dark energy, e.g. from type Ia supernovae 2000 Detection of “acoustic peaks” in CMB power spectrum by balloon experiments 2003 announcement of results of WMAP satellite The cosmic microwave background photons were last scattered when the Universe was only 380 000 years old. Scales/Distances Earth Moon Sun 1.3 x 107 m 3.6 x 106 m 1.4 x 109 m distance to Sun 1.5 x 1011m centauri Galactic centre M31 Andromeda 4.0 x 1016 m 2.6 x 1020 m 2.2 x 1022 m Virgo cluster 4.6 x 1023 m Hubble radius 1.4 x 1026 m 1 parsec =3.08 x 1016 m pc, kpc, Mpc, Gpc k kilo 103 M Mega 106 G Giga 109 Cosmological Principles • Copernican Principle: Earth is not at the centre of the Universe • Perfect Cosmological Principle: The Universe is homogeneous, isotropic and static . • Anthropic Principle: The Universe must have conditions which are compatible with our existence Multiverses • The Cosmological Principle (agreed upon by most): The Universe is homogeneous and isotropic homogeneous: the same everywhere no point special isotropic: no preferred direction isotropic everywhere homogeneous homogeneous isotropic